The present invention relates to an ink-jet type image-forming apparatus (hereinafter referred to as an xe2x80x9cinkjet imaging apparatusxe2x80x9d) which forms an image by ejecting an ink through a nozzle of a printing head onto a recording medium with the printing head moved in reciprocation in a prescribed main scanning direction.
Ink-jet imaging apparatuses for printing by ejecting ink onto a recording medium are known as a kind of output apparatus of computers and work stations. The ink-jet imaging apparatuses are provided, for example, with a printing head which has plural ink ejection nozzles, a carriage which carries the printing head and is moved in reciprocation in a prescribed main scanning direction, and a delivery device which delivers a recording paper sheet in the direction perpendicular to the main scanning direction.
In formation of an image on a recording paper sheet, the delivery of the recording sheet is temporarily stopped, and ink is ejected through the ink ejection nozzles with the reciprocating movement of the carriage in the main scanning direction to form (to print) one printing band portion of an image on the area of the recording sheet placed on an image formation zone. Then the recording paper sheet is delivered by a distance of one printing band breadth and stopped, and again another printing band portion of an image is formed on the newly delivered area of the recording sheet on the image formation zone. By repeating the operation, an entire image is formed on the recording paper sheet.
Generally, the aforementioned plural nozzles are formed on a plate made of glass, silicon or a like material. In the vicinity of the respective nozzles, a heat-generating element (heat-generating element for image formation) is provided. An aluminum base plate backs the silicon plate for strengthening the silicon plate having the nozzles formed thereon.
In an imaging apparatus for forming an image with an ink like the aforementioned inkjet imaging apparatus, the image formed (printed) continuously can cause deterioration of image quality owing to change of the ink ejection state. The change of the ink ejection state may be caused by bubbling of the ink in the nozzle or invasion of a foreign matter (such as paper dust) into the ink.
For removal of the bubbles and the foreign matter from the nozzles, an ejection recovery system is employed which sucks the bubble and the foreign matter forcibly together with the ink to recover the initial normal state of the ink ejection (a state of no bubble and no foreign mater). This ejection recovery system is employed on detection of abnormal ink ejection or at prescribed time intervals during printing.
The ejection recovery system conducts cleaning by covering the opening of the nozzle formed on the printing head with a rubber cap, applying a negative pressure from the outside to suck the ink from the nozzle. Thereby the initial normal state of ink ejection through the nozzle is recovered.
Inside the printing head, the temperature is controlled to control the quantity of the ink ejected through the nozzle in one ink ejection. Thereby, a constant quantity of the ink is ejected from the printing head independently of the temperature outside the printing head. However, the ink ejection may become irregular or fail by formation and accumulation of a bubble in the nozzle owing to temperature difference between the inside and the outside of the printing head. The aforementioned ejection recovery system is effective to solve such a problem.
However, such an ejection recovery system takes long time for the recovery operation, since the system covers the nozzle outlet with a cap and sucks the ink from the nozzle by application of a negative pressure. Therefore, the recovery operation in each time of ejection failure will decrease the number of printed sheets for a unit time (the throughput being lowered).
In usual printing, the printing head is driven to scan immediately after the delivery of the recording paper sheet by a breadth of one printing band portion. Thereby, the time of the printing is kept constant, and the time interval of joining the front end of the printing region to the rear end of the printed region (joint between the printing bands) is constant. However, when the ejection recovery is conducted during the printing with the ejection recovery system, the time interval of the ink overlapping becomes larger at the adjacent printing band joint portion to change the time before the overlapping of the ink at the band joint portion. In other words, the ejection recovery by the ejection recovery system will lengthen the time of the drying of the ink having deposited at the preceding scanning on the recording paper sheet. This may cause change of the color tone at the ink overlap at the band joint, causing irregularity of color.
The present invention intends to provide an inkjet imaging apparatus which is capable of removing a bubble or a foreign matter from an ink ejection nozzle (ejection recovery) in a shorter time under the aforementioned circumstance.
A first embodiment of the inkjet imaging apparatus of the present invention for achieving the above object has a printing head having plural nozzles for ink ejection, and first ink ejection elements formed respectively near each of the nozzles for ejecting the ink from the nozzle; and forms an image by driving the first ink ejection element to eject the ink, wherein the inkjet imaging apparatus comprises:
(1) second ink ejection elements formed respectively upstream against the ink ejection direction before the first ink ejection element for ejecting the ink from the nozzles, and
(2) a controller which drives, on prescribed ejection recovery, the first ink ejection elements and the second ink ejection elements simultaneously to eject the ink through the nozzles for ink ejection recovery.
A second embodiment of the ink-jet imaging apparatus of the present invention for achieving the above object has a printing head having plural nozzles for ink ejection, and plural ink ejection elements formed respectively near each of the nozzles for ejecting the ink from the nozzle; and forms an image by driving any of the ink ejection elements to eject the ink in accordance with image information signals, wherein the ink-jet imaging apparatus comprises:
(3) a controller which drives, on prescribed ejection recovery, two or more of the ink ejection elements simultaneously to eject the ink through the nozzle for ink ejection recovery.
(4) The controller may function to change timing of ink ejection of the ink ejection element in correspondence with the shape of the ink liquid face at the outlet of the nozzle.
The controller may be provided with
(5) a temperature sensor for detecting the inside temperature of the printing head, and
(6) a controller which drives, on prescribed ejection recovery, both of the first ink ejection element and the second ink ejection element simultaneously at prescribed time intervals intermittently in correspondence with the temperature detected by the temperature sensor to eject the ink through the nozzles.
The above ink-jet imaging apparatus may have
(7) two or more of the printing heads, and
(8) the controller may decide the time interval for each of the printing heads in correspondence with properties of the ink to be ejected from the nozzle of each of the printing heads. The above ink-jet imaging apparatus may have
(9) a memory for memorizing preliminarily the prescribed time interval varying in dependence of the inside temperature of the printing head for each of the inside temperature,
(10) the controller may control both of the first ink ejection element and the second ink ejection element to eject the ink at intervals memorized in the memory based on the inside temperature detected by the temperature sensor, and
(11) the controller may decide the number of times of simultaneous driving of the first ink ejection element and the second ink ejection element based on the temperature detected by the temperature sensor.
The above ink-jet imaging apparatus may have
(12) two or more of the printing heads, and
(13) the controller may decide the above-mentioned number of times for each of the printing heads independently in accordance with properties of the ink to be ejected through the nozzles of each of the printing heads,
(14) The above memory may memorize the number of times of simultaneous driving of the first ink ejection element and the second ink ejection element, varying with the inside temperature of the printing head, and
(15) the controller may control both of the first ink ejection element and the second ink ejection element to eject the ink in the number of times and in the time intervals derived from the memory depending on the inside temperature detected by the temperature sensor.
A third embodiment of the inkjet imaging apparatus of the present invention for achieving the above object has a printing head having plural nozzles for ink ejection, and first ink ejection elements formed respectively near each of the nozzles for ejecting the ink from the nozzle; and forms an image by driving the first ink ejection element to eject the ink, wherein the ink-jet imaging apparatus comprises:
(16) second ink ejection elements formed respectively upstream against the ink ejection direction before the first ink ejection element for ejecting the ink from the nozzles, having higher ink-ejection performance than the first ink ejection elements.
The ink-jet imaging apparatus may have
(17) a controller which drives the first ink ejection elements at a prescribed first timing, and drives the second ink ejection elements at a second timing later than the first timing.
The above inkjet imaging apparatus may have
(18) a counter for counting the number of times of driving of the first ink ejection elements, and
(19) the controller may drive the second ink ejection elements when the count of the counter reaches a prescribed number of the times.
The above ink-jet imaging apparatus may have
(20) a temperature sensor for detecting the inside temperature of the printing head,
(21) the controller may change the number of times of driving of the second ink ejection element in accordance with the temperature detected by the temperature sensor, and
(22) the above ink ejection element may be a heater element which generates heat, or a piezo element which causes a piezo electric effect.